Smart Book 27
Consider a population of crickets that occupies two fields separated by a road and two ditches. Crickets inhabiting the two fields comprise two local populations, or demes. What is the likelihood that a cricket will reproduce within its own deme compared to the likelihood a cricket will reproduce with a cricket from the other deme?
The likelihood of reproducing within a deme is much higher than the likelihood of reproduction between demes.
When individuals migrate, alleles can be transfered from one population to another population. This commonly referred to as ____ ____.
gene flow
The change in a population's gene pool from one generation to the next is known as ______.
microevolution
Disruptive selection typically acts on ______.
quantitative traits that are influenced by more than one gene
Microevolution is best described as ______.
the change in a population's gene pool from generation to generation
You are studying a population of birds that has recently become established on an island some 1,000 km from the mainland. On the mainland, these birds mostly consume fleshy fruits, however, on the island they are forced to eat nuts that have to be cracked open with a strong beak. What type of selection is most likely to occur for genes that determine the size and strength of the beak in these birds?
Directional selection
Which of the following phenomena is responsible for introducing new genetic variation in a population?
Mutation
Two types of factors can govern microevolution. On one hand, mutation is a constant source of new genetic variation. On the other hand, mechanisms, such as natural selection and genetic drift, can act to alter existing genetic variation. How do those two types of factors compare in terms of the magnitude of their effect on allele frequencies in a population?
Mutations have a negligible effect on allelic frequencies, while mechanisms, such as natural selection and drift, can have a dramatic effect.
What is the most common type of polymorphism found in natural populations, including human populations?
SNPs
How is the allele frequency of a population calculated?
The number of copies of the allele in the population is divided by the total number of all the alleles for the same gene in the population.
Stabilizing selection typically acts on quantitative traits determined by multiple genes. Does stabilizing selection have an effect on the genetic diversity of those genes and if so, what type of effect?
Yes, stabilizing selection tends to decrease the genetic diversity of those genes.
The ____ ____ of a population consists of all of the alleles of every gene in all of the individuals of that population.
gene pool
The term genetic ____ refers to any random change in the frequencies of alleles in a population.
genetic drift
____ occurs when two genetically related individuals (for example, cousins) mate.
inbreeding
When two genetically related individuals mate, it is called ____. In contrast, mating between unrelated individuals is known as ____.
inbreeding, outbreeding
Factors such as an individual's fertility and the ability to find a mate contribute to ____ ____.
reproductive success
Mutations occur when the DNA of an organism changes. Changes often happen in gene ____, but may also involve the structure and number of chromosomes.
sequences
A change in one nucleotide in a gene is also known as a ____ -nucleotide ____, or, SNP.
single, polymorphism
In disruptive selection, ______.
two or more alleles are maintained in a heterogeneous environment
Which are required for gene flow to occur?
- Migrants must be fertile and pass their genes to the next generation. - Individuals must migrate from one population to another.
Inbreeding and outbreeding can cause certain features of populations to deviate from Hardy-Weinberg equilibrium. From the list below, choose the statements that describe commonalities between inbreeding and outbreeding. Assume that no other evolutionary processes are acting on the genes in question.
- Neither inbreeding or outbreeding affect the allele frequencies in a population. - Both inbreeding and outbreeding alter the relative proportions of heterozygotes in a population.
Which of the following correctly defines a population of sexually reproducing species for the purposes of population genetics?
A group of individuals that occupy the same area and can interbreed with each other
Which of the following is a situation in which directional selection may be observed?
A new allele, which promotes higher fitness in organisms that carry it, is introduced in a population (for example, by a random mutation).
Consider the following types of changes in DNA: a deletion of part of a gene (A); a duplication of a region in a gene (B); a replacement of one nucleotide with a different one (C). Which of those changes can cause polymorphisms in a population?
A, B, and C
If genetic drift is followed over a great many generations, what is its expected effect on allele frequencies?
Alleles are either lost (frequency of 0%) or fixed (frequency of 100%) in the populations.
Over time, genetic drift can lead to the fixation of an allele. What types of alleles are usually fixed by drift?
Genetic drift is random, so deleterious, beneficial, or neutral alleles can become fixed.
Most mutations are ______.
deleterious or neutral
Population genetics is concerned with the ______.
extent of genetic variation within a group of individuals
A group of individuals from a larger population can migrate to a new area and establish a colony, which will be highly susceptible to genetic drift. This is known as the ______ effect.
founder
Natural selection is the phenomenon in which certain phenotypes have ______ than other phenotypes.
greater reproductive success
A ____ is any change in the DNA of an organism, for example, a change in DNA sequence or the structure and number of chromosomes.
mutation
In ____ assortative mating, individuals tend to choose mates with with similar phenotypes. In ____ assortative mating, individuals tend to choose mates with dissimilar phenotypes.
positive, negative
Genetic drift is the _____ in a population.
random change of allele frequencies
____ selection acts on quantitative traits determined by multiple genes. In this type of selection, individuals with intermediate phenotypes have higher fitness and are selected for, while extreme phenotypes are selected against.
stabilizing
Choose the two most important results of the founder effect on the newly founded population.
- The founding population typically has less genetic diversity than the original population. - The founding population typically has very different allele frequencies from those of the original population.
In order to derive the Hardy-Weinberg equation, the two scientists assumed that ______ population's gene pool..
gametes are independently chosen at random from the
Consider a population and a gene that has two alleles in this population, designated as D and d. If you divide the number of individuals with the genotype DD by the total number of individuals in the population, you will calculate the ______.
genotype frequency of the DD genotype
A large, healthy, natural population typically exhibits a ______ level of SNPs.
high
According to the theory of ____ ____, individuals with alleles leading to greater reproductive success will be more likely to produce offspring and pass those alleles to the next generation.
natural selection
Which of the following is an accurate depiction of the Hardy-Weinberg equation for a gene with two alleles?
p2 + 2pq + q2 = 1
Most of the traits in a healthy natural population exhibit some level of variation, or ____, that is, they are found in two or more forms.
polymorphism
Which of the following are factors that can cause a change in the size of a population from one generation to the next?
Predators Diseases Natural disasters
Consider a population of cheetahs, inhabiting a protected area in Africa. In 2012, there were 112 cheetahs in this population. During that year, 60 of those animals reproduced and 48 new cubs were born. What constitutes the gene pool of the new generation made of those 48 new cubs?
All of the alleles of all the genes that were passed from the 60 parents to the 48 new cubs
Natural populations are dynamic entities. From the list below choose features of populations that can change from one generation to the next.
Geographic location Genetic composition Size
The weight of a human baby at birth is a quantitative trait determined by the activity of many genes. Babies with very low or very high birth weights have a decreased chance of survival, while babies with intermediate birth weights have much better chances of survival. What can you hypothesize about the genetic diversity of genes that determine birth weight in humans?
They are under stabilizing selection, which should decrease their genetic diversity.
A founding population usually has lower genetic diversity than the original population it came from. For those alleles that are shared by the two populations, how are allele frequencies different (or similar)?
Usually, the allele frequencies in the founding population are very different from those of the original population.
Consider a population and a gene that has two alleles in this population, designated as E and e. If you divide the number of all the copies of the e allele in the population by the total number of copies of both alleles (E and e) in the population, you will calculate the ______.
allele frequency of the e allele
For random mating to occur, individuals must choose their mates irrespective of their genotype/phenotype. When this condition is violated, non-random mating is occurring, also known as ____ mating.
assortative
In ____ selection, natural selection favors the maintenance of two or more alleles in a population. An example of that is the phenomenon of heterozygote advantage.
balancing
In certain populations, natural selection can favor the maintenance of 2 or more alleles in a population. An example of this is ______ selection.
balancing
A healthy population can become highly susceptible to genetic drift if its size is dramatically reduced due to natural phenomena, such as earthquakes or droughts. This is known as the ______ effect.
bottleneck
The ____ effect is observed when a population's size is dramatically reduced due to natural events, such as earthquakes and flood, or due to human destruction of habitat.
bottleneck
In ____ selection, individuals at one extreme of a phenotypic distribution are more likely to survive and reproduce in a particular environment.
directional
Sometimes individuals at one extreme of a phenotypic distribution are favored in a particular environment, for example, selection will strongly favor insects that have very high resistance to an insecticide. In such cases, the type of selection that operates is ______ selection.
directional
Some traits are quantitative, i.e. they are determined by multiple genes and exhibit a range of phenotypes. For some of those traits, the fitness values for particular genotypes may be higher in one environment and lower in another. When populations with such traits inhabit heterogeneous environments, multiple alleles can be maintained through the action of ______.
diversifying
A population that has experienced a bottleneck is highly susceptible to genetic drift ______.
during the initial bottleneck and during the generations following the bottleneck when the population size is small
Sometimes populations become susceptible to genetic drift via the ____ effect. This happens when a small group of individuals separates from a larger population and migrates to a different site, where it establishes a colony.
founder
New mutations can be deleterious, neutral, or beneficial. Which of those three general types of mutations are most likely to occur?
Deleterious and neutral mutations are much more likely than beneficial mutations.
Which type of selection is also known as diversifying selection because it tends to favor the survival of two or more different phenotypes in a heterogeneous environment?
Disruptive selection
True or false: In a large population made of several local populations, the likelihood of breeding within a local population is roughly the same as the likelihood of breeding with an individual from a different local population.
False
When scientists study populations, they typically observe high levels of variation in many of the traits that characterize a species. In genetics, variations in traits at the population level are known as ______.
polymorphisms
In genetics, a ____ of a sexually reproducing species consists of a group of individuals of that species, which occupy the same region, and can successfully interbreed with each other.
population
The genetics field that is concerned with the extent of genetic variation within a group of individuals and changes in that variation over time is ____ genetics.
population
Which factors contribute to reproductive success?
Having high fertility Having characteristics that make an individual better adapted to the environment The ability to find a mate
You are observing two populations of the same animal species. Population 1 consists of 46 individuals, while population 2 consists of 3325 individuals. Which population is more susceptible to genetic drift?
Population 1 is more susceptible.
Which type of selection tends to select against extreme phenotypes for a quantitative trait, because individuals with intermediate phenotypes have the highest relative fitness values?
Stabilizing selection
A scientist is studying two populations of the same species of birds - one in Michigan and one in Montana. Both populations are relatively large (with more than 10,000 individuals each). However, the Michigan population has a much lower genetic diversity than the Montana population. Which of the two populations is most likely to have experienced a bottleneck and which of the two populations is currently more susceptible to genetic drift?
The Michigan population likely experienced a bottleneck in the past. Both populations are equally susceptible to genetic drift.
How can we calculate the frequency of a specific genotype in a population?
The number of individuals with this genotype in the population is divided by the total number of individuals in the population.
